Straight potentiometer with linear motion contact



Jan. 2, 1968 M. w. BANG 3,362,004

STRAIGHT POTENTIOMETER WITH LINEAR MOTION CONTACT Filed March 30, 1966 4 Sheets-Sheet 1 I N VE N TOR MOGE/VS W. 5,4/v6

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M. w. BANG 3,362,004

R MOTION CONTACT Jan. 2; 1968 STRAIGHT POTENTIOMETER WITH LINEA 4 Sheets-Sheet Z Filed March 30, 1966 INVENTOR. M06N5 l1. BANG M. w. BANG 3,362,004

STRAIGHT POTENTIOMETER WITH LINEAR MOTION CONTACT Jan. 2, 1968 4 Sheets-Sheet 4 INVENTOR.

MOGE/VS M 54/VG ATTORA/EKS Filed March 30, 1966 mxzmw, wawzm United States Patent 3,362,004 STRAIGHT POTENTIOMETER WITH LINEAR MOTION CONTACT Mogens W. Bang, Ridgway, Pa., assignor to Stackpole Carbon Company, St. Marys, Pa, a corporation of Pennsylvania Filed Mar. 30, 1966, Ser. No. 538,761 9 Claims. (Cl. 338-183) ABSTRACT OF THE DISCLOSURE Parallel spaced collector and resistance strips are electrically connected by a flexible wire coil slidable lengthwise of the strips to vary the resistance. The coil encircles a post that is movable lengthwise of the strips by means of a slide mounted in a longitudinal slot in one wall of the housing containing the strips.

It is among the objects of this invention to provide a linear potentiometer which can be assembled quickly and inexpensively, which requires no riveting or crimping of resistance element or terminals, which allows the resistance element to shrink without losing contact with its terminals, which has fewer parts and requires fewer assembly operations than heretofore, which contains a movable contact member that engages the adjoining collector and resistance element at a multiplicity of points simultaneously, which is designed to have the terminals project from either one end or the back of its housing, and which can be mounted individually or be readily attached to a bracket that can be mounted on a perforated circuit board.

In accordance with this invention the potentiometer has an elongated housing provided with a front and a back connected by side walls. A resistance strip is disposed inside the housing against one side wall. Electric terminals engaging the opposite ends of the strip extend out of the housing. A collector strip is disposed in the housing against the other side wall parallel to the resistance strip and is provided with a terminal likewise extending out of the housing. The housing is formed so that all of the terminals can project either from one end or from the back. The front of the housing is provided with a central longitudinal slot. Mounted in this slot is a slide that is movable lengthwise of the housing. The slide has a post extending across the two strips in the housing. The post is spaced from both strips and is encircled by a flexible wire coil that is spaced from opposite sides of the post. The coil presses against the resistance and collector strips to electrically connect them as the slide is moved along the slot. Preferably, each of the terminals fastened to the resistor strip is itself a narrower metal strip which has an inner end portion bent upon itself to form a U-shape clamp that tightly receives a portion of the resistor strip.

The invention is illustrated in the accompanying drawings, in which FIG. 1 is an isometric view showing the terminals projecting from one end of the potentiometer housing;

FIG. 2 is an isometric view showing the terminals projecting from the back or bottom of the housing;

FIG. 3 is an enlarged longitudinal section of FIG. 1 with the front or upper wall removed to show the inside of the housing;

FIGS. 4 and 5 are longitudinal sections taken on the lines IV-IV and VV, respectively, of FIG. 3;

3,362,004 Patented Jan. 2, 1968 FIG. 6 is a cross section taken on the line VIVI of FIG. 4;

FIG. 7 is a cross section taken on the line VII-VII of FIG. 5;

FIG. 8 is a view similar to FIG. 4, but showing the potentiometer of FIG. 2 with parts of the collector strip broken away;

FIG. 9 is a fragmentary end view of a modification;

FIG. 10 is a fragmentary longitudinal section taken on the line XX of FIG. 9;

FIG. 11 is a fragmentary rear view of a gang of potentiometers connected to a bracket mounted on a perforated circuit board;

FIG. 12 is an end view of the bracket with the potentiometers connected to it; 7

FIG. 13 is a view of the upper end of the potentiometer shown in FIG. 12;

FIG. 14 is a view of the upper end of a potentiometer connected to a supporting panel at its front;

FIGS. 15 and 16 are enlarged fragmentary longitudinal sections of two further embodiments of the invention mounted on circuit boards; and

FIG. 17 is a fragmentary detail showing a modified terminal member. 7

Referring to FIGS. 1 to 7 of the drawings, the elongated rectangular housing 1 of the potentiometer may be formed of a molded plastic or other suitable rigid material. The front or top of the housing is provided with a central longitudinal slot 2 through it that extends nearly the full length of the housing. The housing referably is made from two molded half sections that have meeting edges extending from front to back across the end walls of the housing and lengthwise along its back or bottom. The half sections may be joined together along their meeting edges by an adhesive or, preferably, the half sections can be held tightly together by a spring clip 3 snapped into recesses 4 in the back and side walls of the sections. The ends of the clips are turned inward to engage ledges 5 in the recesses as shown in FIG. 6.

Each of the meeting edges of the half sections is provided with notches 6 and tongues 7. The tongues on each half section fit in the notches in the other half section so that the two sections interlock with each other. In accordance with this invention, the tongues are shorter than the notches so that rectangular openings 8 are left at the outer ends of the tongues for a purpose to be described. A similar opening 9 extends through each end wall of the housing at the samelevel as the. adjoining inner surface of the back wall. This opening is formed partly in each half section of the housing.

Disposed inside the housing, flat against one side wall, is a straight fiat strip 10 to which electrical resistance material has been applied. The material can be applied to both surfaces of the strip or only to the surface facing the opposite side of the housing. Current flow is evenly distributed across the width of the resistance element, so there is better heat distribution than with circular elements where current flow is heavy along the inside edge and light along the outer edge. Also, much less scrap is formed in making a straight element than in the case of a circular element.

Electric terminals are connected to opposite ends of strip 10 and extend out of the housing. Assuming that the terminals are to project from one end of the housing as shown in FIG. 1, the terminal at that end of the resistance strip is formed from a narrow strip of metal, the inner end portion of which is doubled upon itself to form a U-shape spring clamp 11 as shown in FIGS. and 7, which receives and tightly engages the opposite Sides of the adjoining end of the resistance strip when the strip is forced into the clamp. The open end of the clamp is adjacent the front of the housing. The outer side of the clamp fits in a recess 12 in the adjoining side wall of the housing and has an integral extension 13 on its upper end that extends at right angles out of the adjoining end of the housing through the opening 8 nearest the front wall of the housing. The projecting portion of the terminal has lateral projections 14 that engage the outer surface of the end wall and thereby prevent the terminal from being pushed into the housing.

The terminal at the opposite end of the resistance strip likewise has a clamping portion 15 that clamps onto the strip. However, the open end of the clamp is adjacent the back of the housing as shown in FIGS. 5 and 6. The outer portion of the clamp fits in a recess 16 in the adjoining side wall, but extends inwardly beneath the resistance strip and then joins one edge of a long straight portion 17 of the terminal as shown in FIG. 3 that extends along the back of the housing toward the far end and out through opening 9. This terminal also has an ear 18 (FIG. 5) that projects into the other opening 9, as shown in FIG. 5, to help hold the terminal. Preferably, the inside of the back wall of the housing is provided with a pair of laterally spaced ledges 19 integral with the side walls also. These ledges stop short of the clamping portions of the terminals. The long part 17 of the one terminal fits between the two ledges, and the resistance strip rests on one of them. The spring-clamp terminals grip the resistance element tightly even if its substrate shrinks. They require no riveting or crimping to hold them in place. By their use, several parts and assembly operations that have been required heretofore are eliminated.

Disposed flat against the inner surface of the other side wall of the housing is a metal collector strip 20, which is provided at one end with an integral terminal 21 that extends out through an opening 8 in the same end wall as the other two terminals. The opposite end of the collector strip is provided with an ear 22 that projects into opening 8 in the opposite end of the housing, as shown in FIG. 4. This strip rests on the underlying ledge 19 and has ears 23 that project into the back openings 8 at the opposite ends of this ledge. There is no problem in assembling the strips and terminals with the housing, because it is done before the two half sections of the housing are joined together.

Movable lengthwise of the housing is a slide 25, opposite sides of which are provided with parallel longtiudinal grooves 26 as shown in FIG. 6 that receive the side walls of the slot 2 in the front of the housing, whereby the slide is locked in the housing but can be moved back and forth along the slot. The slide has an actuating knob that projects from the housing. This slide carries a contact member that engages the resistance strip and the collector strip to electrically connect them. A feature of this invention is that the contact member is a flexible metal coil 27 mounted on a post 28 projecting from the slide into the space between the two straight strips. The width or thickness of the post transversely of the housing is considerably less than the inside diameter of the coil so that the coil will be spaced from opposite sides of the post and can be compressed slightly by the two strips that it engages as shown in FIG. 6. On the other hand, the width of the post lengthwise of the housing is substantially equal to the inner diameter of the coil, as shown in FIG. 5, to avoid loose play between these two elements as the slide is moved back and forth. The coil may be retained on the post by providing the inner end of the post with a head 29. As the slide is moved along the slot in the housing, each of the two strips that the wire coil presses against will be slidingly engaged by each convolution of the coil. This means that each strip is engaged at a multiplicity of points on the coil so that good contact is always present. The multiple contacts also reduce contact resistance and contact pressure and thus reduce wear of the resistance element and noise while improving heat dissipation from the element. The multiple spiral contacts of the coil again-st the resistance element adjust to surface irrgularities and provide smooth rounded contact surfaces.

The housing side wall engaged by the resistance element may be provided with one or more openings 30 that provide cooling of the element without exposing the resistance material when the coating is only on the inner surface of strip 10. The strip can be provided with color coding visible through the housing openings.

The potentiometer just described, with all three terminals projecting from one end of the housing, is mounted in a perforated circuit board 31, as shown in FIGS. 11 and 12, by merely aligning the three terminals with three holes in the board and then inserting them. This potentiometer, due to its construction, is especially suitable for use with other like units in a gang that can be rigidly connected together by mounting them in a metal bracket. Such a bracket may include a flat plate 32 provided with rectangular holes 33 for receiving rearwardly projecting spring loops 3d integral with modified clips 35 that hold the half sections of the potentiometers together. Each loop expands after being pushed through a bracket hole 33 and thereby locks the potentiometer against the plate 32. The opposite ends of the plate are connected to resilient legs 36 that have ends adjacent the potentiometer terminals for insertion in holes 37 in the circuit board. By providing these free ends of the bracket legs with lateral projections 38 that can engage the lower surface of the board after the bracket has been applied to it, the potentiometers are locked in place. A gang of such potentiometers requires considerably less space than .an equal number of circular potentiometers having the same capacity.

The clips 35 can also serve to ground shielding of the potentiometer. Shielding can be provided by metal plating the plastic housings or by providing the clips with extensions along the outer surfaces of the housings.

When a clip 3 is used, the potentiometer can be mounted on a front panel 40 provided with a slot for movement of slide 25, and central notches 41 for receiving and holding the opposite ends of a large spring clip 42 that covers clip 3 and projects forward through the panel from opposite sides of the potentiometer housing as shown in FIG. 14.

In case it is desired to mount these potentiometers parallel to a circuit board instead of perpendicular to it as shown in FIGURES 11 and 12, the terminals are brought out of the back or bottom of the housing 1 as shown in FIGS. 2 and 8. In this case the two terminals 44- that clamp onto the opposite ends of the resistance strip 10 are identical in shape and both extend out of the bottom of the housing through two of the openings 8 formed at the outer ends of tongues 7. The open ends of the clamping portions of these two terminals are adjacent the lower wall of the housing. The metal collector strip 45 has an integral terminal 46 that also extends through one of the openings in the lower wall of the housing. This strip also is provided with integral ears 47 and 48 that project into other openings '8 in the end walls and back of the housing to help hold the collector strip in place. Otherwise, this potentiometer is the same as the one described first. It will be observed that the same housing can be used for either type and that the resistance strips are the same for both. The only differences are in the terminals for the resistance strip and the position of the terminal on the collector strip. For easier handling, a gang of these potentiometers can be fastened to a mounting plate in the same manner as previously described.

To permit extremely fine adjustment of the potentiometer, it may be provided with a slide 50, as shown in FIG. 10, having a threaded opening through it which receives an adjusting screw 51. The ends of this screw are rotatably mounted in openings 52 in parallel extensions 53 of the end walls of the potentiometer housing. The head of the screw prevents axial movement of the screw in one direction, while a collar 54 on the screw prevents movement in the opposite direction. Therefore, when the screw is turned, the slide will be moved lengthwise of the housing in one direction or the other. The threaded portion of the slide may be split at its top lengthwise of the slide so that the two parts can be spread apart slightly by the screw if it is turned further after the slide reaches the end of its path of travel, whereby the screw threads can slip in the slide without causing any damage. Also, by offsetting the threads in the two parts of the threaded opening, backlash of the slide when the screw is turned can be prevented.

Where a bracket is not used for locking the end terminal type potentiometers on a circuit board, it may be desirable to stabilize a potentiometer by providing it with another point of support behind it. This can be done, as shown in FIG. 15, by providing the collector strip 55 with an integral stabilizing member 56 that extends out of the back of the housing 1 from one of the collector ears 23 and then lengthwise of the housing and beyond the adjacent end in parallel relation to the projecting terminals. The stabilizing member is made more rigid by integrally connecting it to the collector strip terminal 21 by a tying strip 57. The stabilizing member has a portion 58 that is inserted in a hole in the circuit board 59 when the terminals are inserted. The potentiometer therefore is connected to the board at four different points for better stability.

An individual potentiometer, unconnected to a bracket, can be locked to a circuit board by changing the length and shape of the long terminal that extends along the inside of the back of the housing. As shown in FIG. 16, instead of having this terminal 60 project from the lower end of the housing, it is provided with a right angle bend above the lower car '23 of the collector strip and led out through a special hole 61 in the back of the housing. The terminal strip then is bent so that it will extend downwardly and rearwar-dly at an inclination and then straight down through a hole 62 in the circuit board 63. The portion of this terminal strip directly above the board is provided with lateral projections that form shoulders 64 engaging the upper surface of the board at opposite sides of the hole. Immediately below the board the terminal strip is bent to form another shoulder 65 that snaps under the board and engages its lower surface. Thus, the long terminal strip locks the potentiometer to the circuit board, but the potentiometer can be released by springing the terminal strip backwardly away from the other terminals so that it can be lifted out of the hole in the circuit board.

If desired, the resistance element terminals can be made like the one shown in FIG. 17, wherein a narrow flat metal strip 70 has a spring tongue 71 struck out of its inner end portion. This tongue and the opposed part of the terminal straddle and tightly clamp a resistance element strip 72 between them.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A linear potentiometer comprising an elongated housing having a front and a back connected by side walls, a resistance strip disposed inside the housing against one side wall, electric terminals engaging the opposite ends of the strip and extending out of the housing, a

collector strip disposed inside the housing against the other side wall parallel to the resistance strip and provided with a terminal extending out of the housing, the front of the housing being provided with a central longitudinal slot therethrough, a slide mounted in said slot and movable lengthwise thereof, the slide having a post extending across said strips and spaced from both, and a flexible wire coil encircling said post and spaced from the opposite sides thereof, the coil pressing against said strips to electrically connect them as the slide is moved along the slot.

2. A linear potentiometer according to claim 1, in which each of said resistor strip terminals is a metal strip having an inner end portion provided with a struck-out tongue forming with said portion a clamp that tightly receives a portion of the resistor strip.

3. A linear potentiometer according to claim 1, in which each of said resistor strip terminals is a metal strip having an inner end portion secured to a portion of the resistor strip, the remaining portion of one of the resistor strip terminals extends out of the adjacent end of the housing, and the remaining portion of the other resistor strip terminal extends from its inner portion lengthwise along the inner surface of the back of the housing between the resistor and collector strips and out of said end of the housing.

4. A linear potentiometer according to claim 1, in which the width of said post lengthwise of the housing is substantially equal to the inside diameter of said coil, but the width of the post transversely of the housing is considerably less than said diameter to permit the coil to be compressed by the two strips engaging it.

5. A linear potentiometer according to claim '1, in which said housing also has end walls and is formed from two half sections joined together along meeting edges extending from front to back across said end walls and lengthwise along said back, each of said meeting edges being provided with notches and with tongues, the tongues on each half section fitting in the notches in the other half section, said tongues being shorter than said notches to leave an opening at the outer end of each tongue, and said terminals extend through at least some of said openings.

6. A linear potentiometer according to claim '1, in which all of said terminals project from one end of the housing in parallel relation, and said collector strip is provided with a stabilizing member integral therewith extending out of the back of the housing and then lengthwise of the housing and beyond said end of the housing parallel to the projecting terminals.

7. A linear potentiometer according to claim 1, in which each of said resistor strip terminals is a metal strip having an inner end portion secured to a portion of the resistor strip, the remaining portion of one of the resistor strip terminals extends out of the adjacent end of the housing, and the remaining portion of the other resistor strip terminal extends from its inner portion lengthwise along the inner surface of the back of the housing between the resistor and collector strips and out of said back and lengthwise thereof beyond said end of the housing, the portion of said last-mentioned terminal beyond said housing end being provided with spaced shoulders for engaging opposite sides of a supporting panel provided with a hole for receiving that terminal.

8. A linear potentiometer according to claim 1, in which said housing is formed from two half sections having meeting edges, and a U-shape spring clip straddles the housing and presses said sections together.

9. A linear potentiometer according to claim 1, in which said housing is formed from two half sections having meeting edges, and a U-shape spring clip straddles the housing and presses said sections together, the clip being provided with an integral spring loop projecting from the back of the housing, and the potentiometer being in combination with a mounting bracket provided with a hole through which said spring 100p extends to hold the potentiometer against the bracket.

References Cited UNITED STATES PATENTS Daily et a1. 338183 10 8 3,284,697 11/1966 May 338-180 X 3,307,133 2/1967 Wolff 338-1 83 X 3,316,375 4/1967 Tyler et a1. 200168 FOREIGN PATENTS 680,809 2/1964 Canada.

ROBERT K. SCHAEFER, Primary Examiner.

H. HOHAUSER, Assistant Examiner. 

